Hello there!I would like to ask you if there is the possibility to control position of a DC motor using a potentiometer connected to the motor shaft.Can somebody explain me step by step how to do this ?, it is the first time I'm working with Arduino. I know how a PID controller can be applied.I have to use the following materials:

DC Motor (7V)Potentiometer (I can turn it from 0 to 300 degrees)transistordioderesistorExternal adapterMotor shield for Arduino

You seem to have some bizarre expectation of the potentiometer. The motor could turn the potentiometer as it turns. Then, the potentiometer reading would relate to motor position. If the motor doesn't turn the potentiometer, then the potentiometer won't tell you squat about where the motor is.